An RFS Guide to Common Public Interface PanelsThe population’s dependence on high-speed wireless communications continues to

increase with no end in sight. Overcome densification challenges, migrate to 5G and

future-proof your network for C-RAN with end-to-end flexible CPRI solutions from RFS.

RFS introduces its new CPRI panel thatenables easy RF over CPRI testing atthe bottom of the tower, reducing theneed for unnecessary tower climbs, thus minimizing maintenance costs and overall OPEX for customers.

REDUCE TOWER CLIMBS, GET READY FOR C-RAN AND CARVE THE PATH TO 5Gwith CPRI tower solutions.

CPRI OverviewCPRI provides an interface between Optical Base Band Units

(BBU) and Remote Radio Heads (RRH), allowing cell operations and

system performance engineers to ensure the best performance

without having to disconnect the fiber optical system or disrupt

service. Hybrid towers have a distributed architecture where the

base-station transceiver subsystem (BTS) is composed of both BBU

and RRH.

Traditionally, base transceiver stations (BTSs) consisted of the two

functional units: the base band unit (BBU) at the bottom of the

tower and the radio head unit (RRH) at the top of the tower- close

to the antennas. The BBU connects to the network via the backhaul

and to the RRH via Fronthaul.

The RRH transmits and receives the carrier signal that is transmit-

ted over the air to the end user smartphone.

• Baseband unit (BBU) performing base band functions in the

digital domain and located at the base of the tower.

• Remote radio head (RRH) performing radio frequency (RF)

functions on an analog domain located next to the antennas at

the top of the tower.

• This architecture creates challenges for cell site for installa-

tion, maintenance and testing since both units communicate in

different language.

REDUCE TOWER CLIMBS, GET READY FOR C-RAN AND CARVE THE PATH TO 5G WITH CPRI PANEL SOLUTIONS FROM RFSRFS’ new Common Public Radio Interface (CPRI) panel enables easy RF over CPRI testing at the bottom of the tower, reducing the need for unnecessary tower climbs, to minimize maintenance costs and overall OPEX for customers.

An RFS Guide to Common Public Radio Interface Panels

The advent of C-RAN, in conjunction with fiber and CPRI, gives MNOs the ability to centralize base station deployments up to 40 km away, enabling low-cost, highly reliable, low-latency and high-bandwidth interconnected networks.

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Migrate to 5G and future-proof your network for C-RAN with end-to-end CPRI solutions

For more information, visit www.rfsworld.com, or follow us on Twitter: www.twitter.com/RFSworld.

• The BBU and RRH communicate via a standard interface

called Common Public Radio Interface (CPRI). It functions as a

translator that speaks both analog and digital languages.

It is imperative to understand that the ability to detect interfer-

ence can be a challenging and expensive task on cell sites where RF

access is only available at the top of the tower at the RRHs. In fact,

testing requires costly tower climbing crews.

Operators are looking for more cost-effective ground-based test

methods, and CPRI provides that tool. CPRI links allow RF mea-

surements and provide a powerful tool for detecting interference

and PIM without climbing the tower. This has significant benefits,

including eliminating cell tower climbs, improving safety, and mini-

mizing maintenance time and operational expenses.

RF over CPRI (RFoCPRI) allows testing to be done at the base of

the tower, minimizing tower climbs and reducing maintenance

and troubleshooting expenses. RFoCPRI allows RF maintenance

and troubleshooting activities to be performed via fiber coupling

at the BBU. In a nutshell, RFoCPRI allows performing RF testing

at the BBU level, thus performing RRH functional test by

emulating the BBU.

Why CPRI Testing?It is recommended that technicians perform some basic tests.

Starting with an inspection and validation of fiber/connectors,

technicians can isolate any issues with dirty connectors and/or

fiber damage. Following these tests, a CPRI test will be needed in

order to verify that the RRH is operational and that the correct

optics are installed.

It is extremely important to have a smooth process with no installa-

tion failures. Because of the special skills and certification needed

for tower climbing, unnecessary field errors can be quite costly.

Therefore, it is essential to have tools and procedures to conduct

tests from the bottom of the tower – and CPRI is the only test

interface available at the bottom of the tower.

C-RAN Architectures and CPRIA Centralized Radio Access Network (C-RAN) is an architecture

where the BBUs are placed at a centralized location, and the RRUs

are placed at distances up to several kilometers away from the

baseband site. The connection from a BBU to a remote radio unit

is typically a fiber facility which is referred to as “fronthaul” to

differentiate it from backhaul which connects the baseband unit to

the network.

With the significant growth in mobile data traffic, operators are

moving baseband units (BBU) from macro cell sites to a central lo-

cation, allowing greater flexibility and cost savings. The connection

from the BBU to the Remote Radio Head (RRH) is most commonly

via CPRI.

Base Station Hotel

BBU

CPRI

BBU

CPRI

BBU

CPRI

BBU

CPRI

CPRIJUMPERS

MACRO SITE

DARKFIBER

FMU

ADAPTERROUTER

DARKFIBER

HYBRIFLEXHYBRIDCABLE

RRH

BBU

CPRI

FIBERJUMPERS

BBU

CPRI

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One of the primary reasons to use C-RAN architecture with CPRI

fronthaul is to enable the coordination between a mixed – also

called Heterogeneous – network (Het-Net) that combines small

cells to improve the coverage and traditional macro to increase ca-

pacity provided by base stations. In the network, several small cells

can be distributed within the area covered by a macro cell, sharing

the same frequency bands, to fill in the gaps in coverage and to pro-

vide extra capacity. The process of organizing macro cells and small

cells is called SON- Self Organizing/Self Optimization Network.

This becomes critical when more macro and small cells are intro-

duced into the structure in a process known as densification. The

efficient use of SON can both reduce OPEX and increase capacity.

Technology Solutions to Overcome Capacity ChallengesAs the demand for capacity in city areas has grown and macro cells

have reached its limits, providing services to densely-populated

locations becomes a near necessity. There are two major technolo-

gies to address this issue:

1. Small Cells Technology: Small cells are one major technol-

ogy that is being deployed in significant volumes for dense

cities to increase capacity. Small cells are low-powered access

nodes that function as a base station. They can be mounted on

rooftops and poles without a substantial footprint and utility

cost.

2. CPRI Technology: Unlike a small cell, a distributed system is

deployed in which the RRH remains on the poles, but the BBU

are separated and moved to a location from the bottom of

the structure and placed in central location, BBU Hoteling, a

few kilometers/miles away. Fiber-based CPRI technology lets

the BBU be moved to a central location; this technology was

enabled by CPRI and fiber.

CPRI can be used between one BBU and RRU; or, it can be between

one BBU and multiple RRUs. As we noted earlier, CPRI was origi-

nally designed as an internal interface for radio base stations. The

main function of the CPRI is to enable independent technology

such as RFoCPRI to test and evaluate on both sides of the interface

fronthaul and backhaul.

As a new CPRI role, BBU can be located further away from the

RRU. With CPRI, the link between BBU and RRU can be extended

to several miles allowing the positioning of additional RRU in

densely populated areas where the demand for wireless internet

services may challenge the available capacity of macro cells. The

wireless internet traffic can be offloaded and distributed from

macro cells.

Also, using CPRI technology offers major advantages when deploy-

ing BBUs. Typically BBUs need power and air-conditioning, which

is costly. By not having a BBU at every site, it reduces the power

consumption and footprint. Leasing/purchasing costs are also sig-

nificant contributors to the OpEx/CapEx of cellular networks.

Lowering the equipment footprint and power requirements at the

cell site can result in major savings, especially if the large cabinets

that house the BBU are no longer needed. Furthermore, by stack-

ing BBUs belonging to different RRU in one location it can improve

the utilization and reliability of radio access networks

RFS’ CPRI Panels RFS’ CPRI panels facilitate the connection between the macro

network and small cells. By enabling fiber connectivity to be tested

between optical BBUs and RRHs, these CPRI panels allow cell

operations and system performance engineers to ensure the best

performance without having to disconnect the fiber optical system

or disrupt service.

RFS’ rugged, lightweight aluminum CPRI Interface Panel provides

bidirectional continuity and uniformity in attenuation over the full

CDWM spectrum while utilizing included optical terminators to

Cell Site EquipmentBBU | Air Conditioning | Power Supply

Traditional

RAN Future-Proof

C-RANSite A

Site B Site C

Central Office | Data Center

Site A

Site B Site C

4G, 5GEVOLUTION

BackhaulNETWORK

CPRI

CPRIBBU

BASE STATION

Cell Site EquipmentBBU | Air Conditioning | Power Supply

Cell Site EquipmentBBU | Air Conditioning | Power Supply

For more information, visit www.rfsworld.com, or follow us on Twitter: www.twitter.com/RFSworld.

reduce optical return loss in the communication link. Engineers can

access the transmit data stream or uplink or downlink through a

monitor port that does not affect service, eliminating the complica-

tions and downtime associated with disconnecting the RRH from

the continuous communications optical link.

RFS’ CPRI solution can be purchased with either 1 or 3 factory-

loaded modules, thus allowing up to 18 CPRI ports in only 1 RU

of space, which is the densest and most compact solution in the

market today, fully aligned with C-RAN applications.

The CPRI panel can be bundled with RFS’ high-quality fiber optic

jumpers (available in several length options), providing an end-to-

end solution that includes HYBRIFLEX® fiber-to-the-antenna DC

and F/O solutions.

ConclusionThe advent of new Centralized-RAN (C-RAN) networks, in conjunc-

tion with fiber and CPRI, gives MNOs the ability to transition from

homogeneous to heterogeneous networks and centralize base

station deployments up to 40 km away, enabling low-cost, highly

reliable, low-latency and high-bandwidth interconnected networks

to accommodate increasing data traffic demands.

RFS’ CPRI panel enables easy RF over CPRI testing at the bottom

of the tower, reducing the need for unnecessary tower climbs, thus

minimizing maintenance cost and overall OPEX for customers.

BBU Hotel

A single location that houses the BBUs of many distributed

RRHs, a BBU hotel can be many kilometers from the radio

heads, typically using fibers running CPRI protocols between

the two. By locating multiple BBUs at one location, radio re-

sources can be allocated dynamically as demand changes. The

radios can be mounted closer to the antenna to reduce RF cable

losses and may improve PIM performance.

Macro Cell

Providing network coverage via a high-power base station, the

macro cell may be mounted on a tall building or dedicated tower.

Typically, the base transceiver station (BTS) radios are located

in an equipment room at the tower base or on the rooftop. High-

power radios provide coverage up to 20 km, with a microwave

link or optical fiber serving as the connection back to the core

network.

Small Cell

Small cells are low-power radios used in the cellular network

to provide densification in urban environments over a limited

range of typically 0.5 km to 4 km. Usually; the integrated radio

is mounted on existing street infrastructure, such as lamp posts,

or on the side of a building.

SON

SON enables the efficient use of heterogeneous networks

(HetNets), a mixed network that includes small cells to improve

the coverage and capacity provided by traditional macro base

stations. Several small cells can be distributed within the area

covered by a macro-cell, sharing the same frequency bands, to

fill in the gaps in coverage and to provide extra capacity. The ef-

ficient use of SON can both reduce OPEX and increase capacity.

However, if they evolve in an unplanned manner then problems

may arise. Adequate coordination is essential in order to avoid

capacity reduction. Dynamic adaptation is needed to maximize

the gains that can be obtained.

“ ” By bundling the RFS CPRI with our popular fiber jumpers, we are able to offer our customers a cost-effective ‘whole package’ solution and eliminate any potential compatibility issues that might arise due to different fiber grade.– Mohamed Alameh, Regional Product Manager, RFS

Glossary of Terms